PC Supplies That Protect Home Computers
UPSs Guard Data and Hardware Against Power Surges, Sags, Blackouts
Nov 13, 2008
In the home, many people are using computers, and other electronics such as DVD players, without any protection at all against power blackouts and against the surges, sags, spikes and breaks in utility power. They are running a risk that their work, games, email, programs and anything else they have on their computers will be garbled or destroyed, and that the equipment itself will be irreparably damaged.
Power Disruptions
Personal computers operate on a low voltage. They process data by switching rapidly between one voltage level that designates a logic ‘1’ and another that designates logic ‘0’. The difference between these two voltages is small. A slight surge or sag or sudden rise or fall of voltage from the utility can be enough to overcome this voltage difference and result in a logic error.
Utility supplies were never designed to provide the precise voltages required for delicate digital electronics. Switching and other operations by the utility can cause the slight changes in voltage that can disrupt data.
In buildings such as office blocks and apartments, equipment such as elevators can cause fluctuations in the electrical supply in the building, In single dwellings, air conditioners and other appliances can do the same.
To protect against these disruptions in power, the home computer user needs a power conditioner. To protect against power blackouts, the user needs an uninterruptible power supply (UPS). UPSs also condition against fluctuations.
Standby Power and Uninterruptible Power Supplies (UPS)
The simplest UPS is a standby unit. It feeds power from the utility through a surge suppressor and a filter that, combined, smooth out fluctuations in power and block spikes and surges. At the same time, utility power is fed to a battery charger that maintains the voltage in a battery. The DC output from the battery is fed to an inverter that chops it into pulses and feeds it out as AC.
When utility power fails, a switch automatically transfers the output of the UPS from the utility power to the power from the battery and inverter. The inverter operates only when utility power fails, so that it does not consume energy all the time. The output voltage of the UPS is maintained for as long as the battery can last.
A disadvantage of the standby UPS is that a brief interruption occurs before the switch transfers the output to the power from the battery and inverter. Anyone buying this type must be sure that the computer can operate on its own during this brief period.
In a variation of the standby UPS, the power from the utility and from the battery/inverter is fed out via a ferro-resonant transformer that acts to smooth out fluctuations and can maintain the output voltage during the switching interval.
Line-Interactive UPS
A shorter interruption occurs with a line-interactive UPS. In this, utility power is fed via a switch to a converter and inverter unit which is connected to both the output and a battery. The converter section produces DC to charge the battery and the inverter converts the DC output from the battery into AC. The inverter/converter also contains surge protection and filtering. When utility power fails, the switch opens so that power is drawn from the battery.
Because the battery is always connected to the output, this UPS takes less time to switch from utility to battery power. This type of UPS is recommended for home use, according to The PC Guide, but is suitable also for industrial and commercial use, says manufacturer Always On.
Online or True UPS
Zero transfer time is achieved with a type called online or ‘true’ UPS. In this, power is fed from the utility via a battery charger, a battery and an inverter to the output. The advantage is that power is drawn from the battery whether or not the utility power is charging the battery. The battery and its charger isolate the output from any fluctuations in utility power. There is no switching in the event of utility power failure. Usually, the online UPS contains a standby path consisting of a surge suppressor and filter which is automatically switched in should the battery or inverter fail.
The disadvantage of the online UPS is that it consumes more power and requires bigger, more expensive components than the others because the inverter runs continuously, not just for the periods of power utility failure.
Some UPSs can transmit a signal to the computer when the battery power drops, so that the computer can automatically save data and close down. One new type from American Power Conversion has outputs that power printers and other peripherals and saves energy by automatically switching them to sleep mode when not being used.
Investment in UPS
Power failures are infrequent, but power fluctuations occur often and are undetectable by the ordinary user. Investment in a UPS protects against the seldom but potentially catastrophic power failure, and against the invisible fluctuations that can also cause damage.
